This NIDDK Mentored Research Scientist Development Award application describes a three-year training plan designed to allow me to acquire additional skill and knowledge so that I can transition into directing my own independent and productive research program. In carrying out the proposed research, and by following a carefully mentored career development plan in a collegial research environment, I will add to my scientific repertoire by acquiring expertise in intestinal epithelial injury models and as well as live-cell and super-resolution microscopy. Using this newly acquired expertise, I will establish a scientific niche that will set me apart from my mentors and pave the way to a robust, extramurally funded research program. The research proposed in this application will focus on understanding how colonic stem cells function in repair after epithelial injury. It is known that Egfr signaling is activated after injury and this contributes to repair; however, this activation ad subsequent growth and proliferation, must be tightly regulated to avoid aberrant overgrowth. I have found that an Egfr inhibitor, Lrig1, marks a population of largely quiescent colonic stem cells, unlike the well-characterized, proliferative stem cell population marked by Lgr5. My proposal seeks to clarify the role of both Lrig1+ stem cells, and the role of Lrig1 as a negative regulator of Egfr, in colonic tissue stem cell homeostasis and wound healing. The requirement of stem cell populations in repair after injury has not yet been tested; this is critical to our understanding of the colonic epithelial crypt niche requirements for promoting proper regeneration. My Specific Aims are designed to test my over-arching hypothesis that Lrig1 is expressed in regenerative progenitor cells, in response to an active growth factor signal, such as activated Egfr signaling. In Aim 1, I will eliminate both Lrig1- and Lgr5-expressing stem cells before and after wound healing, to test their requirement in injury repair. I will evaluate initial injury and end-stage wound-repair by histological, molecular, and super-resolution analysis. In Aim 2, to examine the influence of Lrig1 on Egfr in wound healing, I will examine the effects of the absence of Lrig1 in wound healing, using Lrig1 null mice, and use advanced microscopy to examine the dynamics of Egfr activation. With the evolution of tools to manipulate stem cell populations in vivo, only now are the studies proposed here possible. Moreover, Vanderbilt's super-resolution microscopic capabilities will enable me to examine colon cell dynamics in tissue repair after injury at a resolution not previously possible. By coupling sophisticated mouse modeling with super-resolution imaging, the studies proposed here directly test the relationship between Lrig1- and Lgr5-expressing stem cells in injury repair, as well as examine the role of Lrig1 as a negative regulator of Egfr activity in this wound-healing context. The goal of this Mentored Research Scientist Development Award is to develop the expertise that will allow me to run an independent, funded research program that will contribute to improving human health and disease.